The invention relates generally to the field of electrical drives. More particularly, the invention relates to techniques for detecting drive conditions for capacitor bank protection.
Various power systems include power conversion systems such as electric drives and motors which are employed to convert electrical energy into mechanical energy. An electric drive includes a device or group of devices which controls the torque, speed, position, and/or performance of an electric motor. The drive may be connected to a power source such as a battery, a power supply, or an AC generator, and may control the transmission of power from the power source to the motor, which converts the electrical power into mechanical power.
Electrical drives typically include capacitor banks connected in series and/or in parallel to power input lines of a particular drive. Traditionally, a capacitor bank provides reactive power which decreases the current in the upstream lines of the capacitor bank to improve the voltage and power factor of an associated electrical drive. Improving the voltage and power factor of the drive reduces line losses in the drive, thereby improving the efficiency and performance of the drive. Capacitor banks may also be configured as LCL filters for reducing harmonics from alternating currents that power the drive. Capacitor banks often cooperate with additional features to facilitate drive protection. Generally, capacitor banks are coupled with fuses, surge arresters, and protective relays for protecting the electrical drive.
During the operation of the electrical drive, capacitor banks may be susceptible to becoming unbalanced. For example, an unbalanced condition may occur if one of the capacitor units in the capacitor bank fails, or if a fuse operation occurs in a fused bank. Such conditions may result in high voltages on the remaining capacitor units, which may cause damage to the remaining capacitor units or any associated components.
Some drives involve unbalance detection schemes which detect such unbalanced conditions in capacitor banks. Existing methods are typically suitable for detecting unbalanced conditions in certain configurations of capacitor banks (e.g., in grounded and ungrounded system shunt capacitor banks). However, not all types of electrical drives use the same type of capacitor bank configuration. In fact, electrical drives are used for a wide range of industrial applications, and different applications typically use drives having different capacitor bank configurations. For instance, an electrical drive suitable for relatively lower power configurations may use a capacitor bank configuration that is corner-connected. Typical unbalance detection schemes configured for Y-connected capacitor banks may not be suitable for corner connected capacitor banks.